Forecasting fall foes

Knowing when and how to treat common fall weeds can save LCOs time and money.

In most areas of the country, experts believe LCOs will combat the usual suspects.
All photos courtesy of Dr. David Gardner & Dr. Alec Kowalewski

The summer months are winding down and with the emergence of fall comes plenty of seasonal weeds and diseases that lawn care operators will have to keep an eye out for and combat.

Three professors of turfgrass science from across the country have weighed in on which diseases they feel will make the most impact on certain markets this fall, how lawn care operators should go about treating them and when the best time is for treatment.


What to watch out for

All the way up in the Pacific Northwest, Dr. Alec Kowalewski, associate professor at Oregon State University, says he expects “the classic problems” to persist this autumn.

“Most people come fall are dealing with a lot of false dandelion and annual bluegrass coming in,” he says. “The false dandelion is a perennial that does really well in the end of summer and the annual bluegrass is an annual that comes in the winter months.”

With the annual bluegrass, Kowalewski says the problem is most pertinent at the end of summer and early fall.

“The annual bluegrass has really poor summer drought tolerance, so if you get annual bluegrass in your lawn, it’s going to have a tendency to die in the summer months,” he says. “So, then you’ll have dead patches in the lawn.”

Down south, Dr. James Dewey McCurdy, associate professor with Mississippi State University, also says LCOs are in for more of the same as the seasons change.

“I don’t think there’s any real difference than typical years,” he says. “We expect the types of things that are always emerging in the fall. Weeds, particularly annual bluegrass, and we’re certainly faced with a number of pests but fall armyworm are chief among many of our concerns.”

While McCurdy remembers some years where fall armyworm was worse than others, he says it’s usually pretty sporadic and based upon things like environment and precipitation.

“They thrive in lush Bermuda grass,” he says. “And so, we find that with some locations that have experienced prolonged periods of rainfall, we tend to see they are worse in that area as they can have multiple life cycles.

“In our areas down here with more drought prone conditions, where our driest month is October, we see them but once we dry off, we tend to see the problem abate,” McCurdy adds.

McCurdy says as cliché as it sounds, annual bluegrass will be another challenge to expect this fall.

“What makes our industry interesting, are some of the formidable problems that continue to rear their heads and get worse,” he says. “And annual bluegrass is amongst them. Certainly because of herbicide resistance and continued evolution for adapting to various herbicides.”

Dr. David Gardner, professor of turfgrass science at Ohio State University, doesn’t expect too many challenges this fall for LCOs but says they should get ready for some common complaints from customers.

“(The) diseases I expect to be prevalent would be rust and powdery mildew, which are aesthetically displeasing but most of the time, people do not spray a fungicide to control those,” he says. “It might be more of a customer awareness thing.”

Gardner says typically, rust affects perennial ryegrass while powdery mildew disturbs Kentucky bluegrass. He adds both diseases can infect either grass.

“It’s one of those things that’s noticeable especially when walking through the lawns and you’ve got rust and those pustules get on their shoes and turn them orange,” he says. “But both of those diseases are more cosmetic. They don’t really cause damage to the turf. In the 30 years I’ve been in the turf industry, I have not heard of anyone ever applying a fungicide to it. It’s something that people see but not something that they treat.”

In terms of weeds, Gardner foresees the traditional perennials and winter annual broadleaf weeds to make an appearance yet again.

“When it comes to weeds, if they have problems with perennials — like dandelions, white clover, ground ivy and those kind of weeds — fall is actually the best time to try and control those if you want to get more permanent control,” Gardner says. “The other big thing is people have had problems with winter annual broadleaf weeds. So that’s like chickweed and hairy bittercress. Those weeds seem like they’ve become more prevalent in recent years. I attribute that to it’s been a little nicer in the wintertime and a little more hospitable for those to persist vegetatively during winter.”


Annual Bluegrass often dies in the summer.

When to attack

According to Gardner, knowing when to treat certain weeds and diseases is as, or even more critical, than knowing how to effectively treat them.

He suggests prioritizing treatment in the fall over the summer months.

“With a lot of the testing I do in the springtime, what I see is eight to 10 weeks of effectiveness and then the weeds start to grow back,” he says. “But when I make applications in the fall, that tends to be effective for more like 10 to 12 months. It’s a much more effective time of year for controlling broadleaf weeds.”

Gardner says there is a simple scientific reason that treatments are more effective come the fall.

“In the fall, those plants that are perennials are trying to move photosynthates, or food, into those storage organs that are below ground to store for wintertime,” Gardner says. “So, when you spray the herbicide at that time, more of the herbicide translocate below ground. In the springtime it’s just the opposite, the translocation is up out of the ground and so you can’t get as much herbicide into the ground with a springtime application.

“You can get good control of the top growth in the spring, but then the plant wants to come back,” he adds. “In the fall when you get more of the herbicide below ground, that tends to result in more permanent control.”

Kowalewski also advises treating most common weed occurrences in the fall — and getting a head start on some winter weeds as well.

“The best thing to remove perennial weeds like false dandelion are a broadleaf selective herbicide that we typically find is most effective when it’s applied in the fall. Particularly when temperatures are less than 80 degrees and the weeds are actively growing,” he says. “At the same time, if you couple that fall application of the broadleaf herbicide with a pre-emergent herbicide, that will help you control the winter annual and annual bluegrass.”

McCurdy says pinpointing exactly when to treat certain weeds can be challenging and has been ranging over recent years.

“A changing climate and weather patterns associated with that is driving much of what we consider in regard to control,” he says. “Pre-emergence herbicide timing is slightly later in the fall for annual bluegrass and it’s slightly earlier in the spring or winter even for many of those weeds.”


Powdery Mildew

Tips for treatment

The most quintessential piece of treatment advice McCurdy would give LCOs would be avoid sole reliance on herbicides, fungicides and the like.

“Continued use of the same herbicides has obviously led to resistance issues,” he says. “We currently don’t have any new herbicides on the market that are really breaking that cycle. We’ve been using basically the same chemistry for the last 10 years or so.”

However, McCurdy isn’t saying to never use such products but to make sure you’re applying the right products at the right time and sometimes in conjunction with one another.

“One of the best management practices is reliance upon pre-emergent strategies followed by post-emergent strategies,” he says. “Sometimes we combine those treatments and sometimes those treatments are applied separately. The two of them are critical for control.”

Other treatment tips McCurdy has includes having LCOs advocate to clients that they give them input on things like mowing height, fertility and irrigation.

“In the southeast, most of our LCOs don’t have control over things like mowing height and irrigation on many of the properties they manage,” he explains. “I wish they did. Trying to communicate with stakeholders that appropriate mowing height and irrigation are incredibly important. Simply raising mowing height this time of year doesn’t eliminate weeds but certainly reduces weed pressure from annual bluegrass and others emerging in the fall.”


McCurdy adds that proper irrigation plays a huge factor in the health of a lawn.

“Too much water is not just economically and ecologically a bad thing but it’s functionally a bad thing,” he says.

Kowalewski also stresses the importance of irrigation in weed deterrence.

“Summer irrigation is really another important part to have a dense, strong turf that can beat out the drought-tolerant dandelion,” he says. “It’ll keep it nice, dense and thick going into the fall when the bluegrass germinates.”

Additionally, Kowalewski says spring and summertime maintenance will also make an impact on the following fall’s weeds and overall health of the lawn.

“Another common thing people will find in Oregon is if they haven’t done a good job of maintaining their lawn in the summer, they’re going to have weak and poor density,” he says. “Doing your regular fertilization in the spring and the fall keeps your turfgrass healthy as possible. It’s particularly about using fertilizer high in nitrogen. It really helps make the grass strong and be resistant to encroachment of those weeds.”

Gardner adds that a pre-emergence herbicide in the fall can also help combat more problems later in the year.

“You can use the same herbicides you’d use to control crabgrass in the spring,” Gardner says. “You’ll just be making the application in late August or the start of September.”

The author is assistant editor at Lawn & Landscape.

September 2023
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